Air can be made to move by solar energy and the moving air can be directed towards a wind turbine to produce electricity. In solar updraft towers or chimneys, sunshine heats the air beneath a very wide greenhouse-type roofed collector structure (i.e. with transparent and/or glazed panels) surrounding the central base of a very tall chimney tower. The heating causes convection currents which move the air towards the tower by the chimney effect. This airflow drives wind turbines placed in the chimney or around the chimney base to produce electricity. The glazing can consist of a glass or polymer membrane stretched nearly horizontally above the ground. The height of the glazing increases towards the tower base where the heated air is diverted from horizontal into vertical movement with minimum friction loss. The glazing admits the shortwave solar radiation to penetrate and retains long wave re-radiation from the heated ground. Thus the ground under the roof heats up and transfers its heat to the air which enters the circumference of the solar collector array and flows radially to the tower and then rises up the chimney.
However, such greenhouse style collectors used with solar towers have numerous problems that include high costs, very low efficiencies, low temperature rises and large land masses required to generate thermal energy to create sufficient air movement. In other words, very large areas of glazing in the roofs are used to generate the air flow.
Furthermore, the roofs can easily accumulate dust in the large areas, so solar-optical efficiency decreases over time due to dust accumulation and/or the glazing must be cleaned. Furthermore, the durability of such transparent roofs is low as transparent panels are difficult to ruggedize. Further glass panels can be broken easily; and plastic or polymer glazing used as roofs will degrade over time when exposed to UV rays and thin plastic sheets may tear apart under strong wind conditions.
Such roofs also have thermal problems which include low solar efficiencies and low temperature rise which affects the general energy conversion of solar tower or chimney. The low efficiencies require larger solar collector areas to produce more heat and air movement which require higher investment costs.